It is a very well researched book. During reading one is overwhelmed with the immensity of this work. I am not in position, though, to confirm every individual fact mentioned. However, it was a very good decision on my side to take up this book, in order to learn the history of Prussia and more or less the last 400 years of German history.
The impartial attitude of the book was really important for me, which makes it an important reference book for the topic leaning on tons of reference documents. It is basically following the chronological order, which is logical but in some individual instances it was going back and forth a couple years, which was not the best for my taste.
The Second World War is completely left out, which was a perfect decision. I recommend it without doubt, and actually after some time I want to read it once more.
Overall it is a very informative, well structured and surprisingly readable book, but it is a pretty long read.